Alkaline pulping of preimpregnated deciduous wood



Patented June 10, 1952 UNITED STATES PATENT OFFICE 2,599,572 ALKALINE P Lr NG F rntiltirnmmmn DECIDUOUS WOOD Huguenin Miller, Watervliet, assignoito Watervliet reper- Compah'y", Waterviiet, Mich, a corporation of Michigan No Drawing. Application February 1, 1946*, Serial No. 645,005

3 Claims. (01. sit-=13) This invention relates to improvements in alkaline pulping of preimpregnated deciduous wood,

This application is a continuation in part of my application for Letters Patent filed June30, 1943, Serial No. 192,920, now abandoned, and is an adaptation of the method. of my copending application for Letters Patent, Serial No. 641,641, filed January 16, 1946.

The main objects of this invention are:

First, to provide a process of enabling the pulping of deciduous Wood or wood chips such for example as aspen or poplar which results in a relatively high yield of pulp and one in which the lignin content retained in the pulp approximates that of the wood from which the pulp is formed.

Second, to provide a processof pulping wood chips which may be economically practiced on a commercial scale'with satisfactory uniform results and with relatively simple apparatus.

Third, to provide a method of producing a wood pulp which results in a pulp adapted for awide range of uses in the manufacture of paper and paperboard products and even for molding purposes without necessitating the addition of sizing and chemical fixative and purely by mechanical manipulations with standard pulp treating and paper making equipment.

Fourth, to provide a wood pulp assaying ligni'n in a percentage approximately equaling the lignin component of the wood from which the pulp is formed and in which the lignin component is not substantially separated from the fibres.

Fifth, to provide a wood pulp which may be used in the manufacture of sheets having a high degree of moldability, tensile strength, and highly satisfactory burst and tear characteristics.

Further objects and objects relating to details and economies of the invention will appear from the description to follow. The invention is defined in, the claims.

My proce s of producing pulp is well adapted for the producing of a pulp having the adyan tages which I have set forth and others which will appear herein.

In carrying out my process-for example on aspen, the wood is out into chips preferably about three-quarters of an inch long in grain direction. The Wood chips are impregnated with a solution if sodium hydroxide desirably having a concentration of the order of 5%, but under oer tain conditions may range from 2% to approxiniately 6 the concentration of approximately 5% being satisfactory for producing a pulp having a wide range of uses.

The character or condition of the wood may also be taken into consideration in determining the concentration or the solution-for example, old wood, that is, wood that has been cut for some time and become weathered, may require a somewhat heavier concentration than is required for the some kind of Wood which is relatively freshly cut.

In a highly desirable method of practicing the process, the wood chips are immersed in the solution in a closed vessel or retort and the retort or Vessel heated tobring the temperature of the wood chips substantially above boiling temperature and desirably to about 10 above the boiling point of water equivalent to the atmospheric pressure plus the hydrostatic head on the most deeply submerged chips. This temperature with standard types of cookers ranges from 220 F. to 255 F. Very satisfactory results can be accomplished if this temperature is reached in approximately minutes by the introduction of steam, approximately 45 minutes being now regardedby the applicant as minimum. During this heating the vessel or retort is vented at brief intervals to release the air while maintai ing pressure therein. When the chips are heated to the desired temperature the pressure within the vessel or retort is released as rapidly as practical, without substantial. loss of the impregnating solution due to priming, to approximately atmospheric pressure. The chips are allowed to soak for impregnation thereof for approximately 20 minutes or until substantially complete impregnation results. During the period of impregnation substantially atmospheric pressure is maintained within the vessel by the admission of air or additional solution as the Vessel and contents 001. The chips should be thoroughly impregnated with the sodium hydroxide solution, it being the object of this step to secure such, impregnation.

V The period 'of heating the chips may be shortened with steam of higher pressures but it should be understood that the object of this heating and rapid reduction of pressure is to expel air from the chips and get them into condition for the entrance of the sodium hydroxide solution durmg the soaking or impregnating period. The excess or unabsorbed sodium hydroxide solution is then tir'a'wn off the chips and the sam retort or vessel is desirably used for the succeeding step.

Thisimpregnation of the chips is carried on without mechanical fragmentation of the chips. The impregnated chips are then immersed in a water suspension of lime containing lime in excess of the amount required to react with the impregnated chips and to remain in excess throughout the cooking period and while the chips are so immersed. The amount of excess lime is not material so long as a substantial excess is assured or maintained. Ordinarily lime from about 15 to 25% of the oven dry weight of the Wood is employed in the ratio of 150 pounds of hydrated lime to 300 gallons of water.

The retort or digester or closed vessel is then heated, desirably in commercial practice by direct introduction of steam, to a cooking temperature of approximately 280 F., the cooking being continued for about seven hours to render the fibres readily separable by mechanical means. This is found not to substantially reduce the lignin content of the wood or to free the lignin from the fibres which is a highly important and novel feature of the applicants invention.

The batch or charge is then discharged from the retort or digester and washed. The washing may be expedited by subjecting the chips to an attrition mill. The treatment in the attrition mill at this state does not reduce the chips to any substantial quantity of individual fibers, such reduction being specifically avoided inasmuch as it would interfere with the removal of sludge. The attrition mill is so adjusted and used that the chips are partially broken so that deposits of sludge in the cracks or recesses thereof are more thoroughly exposed to the washing and facilitate the removal of the sludge. For the highest yield, water only is used in the washing but for some products an acid may be added to the washing water. After the washing, the fibres are mechanically separated and subjected to such beating and stock treatment as may be desired for the particular product. I have found it practical to use a double disk Bauer pulper for reducing. the washed material to substantially individual fibers.

The time of cooking may be shortened by using higher cooking temperatures but applicant considers it desirable not to exceed 320 E. which is generally regarded as the minimum cooking temperature in the soda process. The fibres produced by applicants method are relatively strong as compared to fibres produced by the so-called soda process. Where a lighter colored pulp is desired, the pulp may be treated with a solution of aluminum sulphate or dilute acid andthen washed. Alkaline hypochlorite solution is suitable for bleaching. However, the washed pulp may go directly to the beater.

The pulp may be beaten to such degree that it possesses superior properties of strength and rigidity, high resistance to penetration by grease r water and even while beaten to that extent has good drainage characteristicsthat is, good performance in the making of sheets.

By this method, I have secured yields of washed unbleached pulp approximately '7 5 of the weight of the Wood.

Paper products from the unbleached pulp assaying lignin in a percentage approximately equal to the lignin component of the wood, the lignin not being substantially separated from the fibres, have many desirable characteristics in addition to their greaseproof character. highly desirable paper may be produced purely by mechanical paper making treatment Without the addition of sizing.

I do not attempt to point out the various possible uses but I have mentioned these uses to bring out that the pulp produced by my method is desirable for use in the manufacture of light papers such as greaseproof papers, printing papers, heavier papers such as wrapping papers and the like, and for molding purposes.

However, where lower concentration of impregnating solutions havebeen used of the order of 2%, the use of acid in the washing water may be found helpful in producing greaseproof paper, for example. When the concentration of impregnating solution is above 5% the yield is normally lower but defibering and refining may be made easier and ordinarily the ease of bleaching is improved by the easier defibering.

Paper made from my pulp has highly desirable'burst and breaking strength qualities. These vary somewhat as would be anticipated by those skilled in the art with variations in the mechanical paper making treatment but it may be generally said that these tests are in general relatively high as compared to products made from pulp produced by methods now in general com mercial practice and receiving the same mechanical paper making treatment. Of course, it will be understood that the applicant has economies which result from being able to produce his products without the addition of sizing and other ingredients commonly used.

It is believed that this disclosure will enable those skilled in the art to practice the method of my invention. It will be understood that the terms and expressions which have been used herein are employed as terms of description and not limitation.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The process of pulping deciduous wood chips which consists of impregnating the chips with a solution of sodium hydroxide having a concentration of approximately 5% by immersing the chips in the solution in a closed vessel, heating in the closed vessel by admission of steam thereto for a period of approximately 90' minutes to raise the temperature of the chips to about 10 F. above the boiling point of water at atmospheric pressure plus the hydrostatic head to which the chips are subject, and venting the vessel at in tervals during such heating to release the air therefrom while maintaining pressure therein, and at the end of such chip heating period releasing the pressure within the vessel rapidly to approximately atmospheric pressure, soaking the chips for impregnation at a temperature below boiling temperature for approximately 20 minutes during which period fluid is admitted sufficient to maintain substantially atmospheric pressure within the vessel, drawing oh the sodium hydroxide solution in excess of that imgregnating the chips, immersing the impregnated chips in a Water suspension of lime sufficient to maintain an excess throughout the subsequent cooking period and while the chips are so immersed, cooking the chips for a period of approximately 7 hOLllS at approximately 280 F. to render the fibres readily separable by mechanical means without substantialy reducing the lignin content of the Wood, and washing in water, and mechanically separating the fibres.

2. The process of pulping deciduous wood chips, which consists of impregnating the chips with a solution of sodium hydroxide having a concentration of about 2 to 6% by immersing the chips in the solution in a closed vessel, heating in the closed vessel to raise the temperature of the chips to approximately 250 F. and venting the vessel at intervals during such heating to release the air therefrom, releasing the pressure within the vessel rapidly to approximately atmospheric pressure, soaking the chips while cooling for impregnation thereof during which impregnating period fluid is admitted sufficient to maintain substantially atmospheric pressure within the vessel, drawing on the sodium hydroxide solution in excess of that impregnating the chips, immersing the impregnated chips in a water suspension of lime containing lime in excess of the amount required to react with the impregnated chips and to remain in excess during the cooking period and while the chips are so immersed, cooking the chips for a period of approximately 7 hours at approximately 280 F. to render the fibres readily separable by mechanical means without substantially reducing the lignin content of the wood, and washing, and mechanically separating the fibres.

3. The process of pulping deciduous wood chips which consists of impregnating the chips with a sodium hydroxide solution having a concentration of approximately 2% to 6% by immersing the chips in the solution in a closed vessel, heating the closed vessel for a period to raise the temperature of the chips to about 10 F. above the boiling point of water at atmospheric pressure plus hydrostatic head on the submerged chips and venting the vessel briefly at intervals during such heating to release the air therefrom while maintaining pressure therein, rapidly releasing the pressure within the vessel to approximately atmospheric pressure, soaking the chips to substantially complete impregnation thereof, drawing 01f the impregnating solution in excess of that impregnating the chips, immersing the impregnated chips in a water suspension of lime, and maintaining an excess of lime throughout the subsequent cooking period and while the chips are so immersed, cooking the chips for such period at a temperature in excess of 212 F. but less than 450 F. so as to'render the fibers readily separable by mechanical means without substantially reducing the lignin content of the wood, and washing and mechanically separating the fibres.

HUGUENIN MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name I Date 878 Holland Aug. 13, 1838 96,239 Keegan Oct. 26, 1869 179,103 Furbish June 27, 1872 1,138,907 Thickens May 11, 1915 1,472,320 Beckman Oct. 30, 1923 1,633,738 Fish June 28, 1927 1,803,443 Hildebrandt May 5, 1931 1,849,334 Richter Mar. 15, 1932 1,880,044 Richter Sept. 27, 1932 1,887,863 Stevenson Nov. 15, 1932 2,169,473 Olsen Aug. 15, 1939 2,228,349 Feldman -1 Jan. 14, 1941 FOREIGN PATENTS Number Country Date 113,503 Australia July 14. 1941 396,284 Germany May 30, 1924 

1. THE PROCESS OF PULPING DECIDUOUS WOOD CHIPS WHICH CONSISTS OF IMPREGNATING THE CHIPS WITH A SOLUTION OF SODIUM HYDROXIDE HAVING A CONCENTRATION OF APPROXIMATELY 5% BY INNERSING THE CHIPS IN THE SOLUTION IN A CLOSED VESSEL, HEATING IN THE CLOSED VESSEL BY ADMISSION OF STEAM THERETO FOR A PERIOD OF APPROXIMATELY 90 MINUTES TO RAISE THE TEMPERATURE OF THE CHIPS TO ABOUT 10* F. ABOVE THE BOILING POINT OF WATER AT ATMOSPHERIC PRESSURE PLUS THE HYDROSTATIC HEAD TO WHICH THE CHIPS ARE SUBJECT, AND VENTING THE VESSEL AT INTERVALS DURING SUCH HEATING TO RELEASE THE AIR THEREFROM WHILE MAINTAINING PRESSURE THEREIN, AND AT THE END OF SUCH CHIP HEATING PERIOD RELEASING THE PRESSURE WITHIN THE VESSEL RAPIDLY TO APPROXIMATELY ATMOSPHERIC PRESSURE, SOAKING THE CHIPS FOR IMPREGNATION AT A TEMPERATURE BELOW BOILING TEMPERATURE FOR APPROXIMATELY 20 MINUTES DURING WHICH PERIOD FLUID IS ADMITTED SUFFICIENT TO MAINTAIN SUBSTANTIALLY ATMOSPHERIC PRESSURE WITHIN THE VESSEL, DRAWING OFF THE SODIUM HYDROXIDE SOLUTION IN EXCESS OF THAT IMGREGNATING THE CHIPS, IMMERSING TH E IMPREGNATED CHIPS IN A WATER SUSPENSION OF LIME SUFFICIENT TO MAINTAIN AN EXCESS THROUGHOUT THE SUBSEQUENT COOKING PERIOD AND WHILE THE CHIPS ARE SO IMMERSED, COOKING PERIOD AND WHILE THE CHIPS OF APPROXIMATELY 7 HOURS AT APPROXIMATELY 280* F. TO RENDER THE FIBERS READILY SEPARABLE BY MECHANICAL MEANS WITHOUT SUBSTANTIALLY REDUCING THE LIGNIN CONTENT OF THE WOOD, AND WASHING IN WATER, AND MECHANICALLY SEPARATING THE FIBRES. 